HOUSING REPORT Steel frame with semi-rigid " Khorjini" connections and jack arch roof " Taagh-e-Zarbi".

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1 World Housing Encyclopedia an Encyclopedia of Housing Construction in Seismically Active Areas of the World an initiative of Earthquake Engineering Research Institute (EERI) and International Association for Earthquake Engineering (IAEE) HOUSING REPORT Steel frame with semi-rigid " Khorjini" connections and jack arch roof " Taagh-e-Zarbi". Report # 25 Report Date Country H ousing Type IRAN Steel Moment Frame Building H ousing Sub-Type Steel Moment Frame Building : Brick masonry infills Author(s) Reviewer(s) Arzhang Alimoradi Farzad Naeim Important This encyclopedia contains information contributed by various earthquake engineering professionals around the world. All opinions, findings, conclusions & recommendations expressed herein are those of the various participants, and do not necessarily reflect the views of the Earthquake Engineering Research Institute, the International Association for Earthquake Engineering, the Engineering Information Foundation, John A. Martin & Associates, Inc. or the participants' organizations. Summary This is a common type of urban/rural construction in many parts of Iran. It is widely used in the cities as a popular structural system for low-rise residential buildings because of the ease of construction and of erecting the frame. Buildings of this type are up to 5 stories high, with a

2 height/width aspect ratio on the order of 1.5. This system consists of a special kind of steel framing with heavy brick infills as partitions. Roof girders are connected to the supporting columns by means of semi-rigid connections. Diaphragms may range from flexible to rigid depending on the detailing and the construction quality. The structure is extremely heavy because of the brick infills between the roof beams. The roof is constructed in the form of a shallow arch called a 'jack arch'. Roofs, ceilings, and floors constructed in this way contributed to building failures and to an unusually high death toll in many recent earthquakes in Iran. As many as half the buildings completed in the early 1970s in Iran had jack arches. In a jack arch system, steel beams or a reinforced concrete joist system span the distance between the main girders across the length of the building. An arch made of small bricks connect the beams. Each arch rises only about ten centimeters. The 'valleys' of this wave-like surface are filled with mortar. The completed ceiling, roof, or floor is thick and heavy. Frequently the steel support beams are not tied together properly or are left untied (From: Seismic vulnerability of this system is observed as medium to high. The dynamic behavior of the system in the two main perpendicular directions of the building plan differs significantly because of the differences in the stiffness and configuration of the connections in these two directions. Furthermore, 'X' bracings are usually used in the weak direction which further magnifies the non-uniform behavior of the structural system. 1. General Information Buildings of this construction type can be found in all parts of Iran. In general, this housing type constitutes 30 to 40% of urban construction types in most of the Iranian cities. However, in northern provinces (Golestan, Mazandaran, Gilan) and in the areas close to the central desert of Iran, (Khorasan, Yazd, and Sistan-va-Baloochestan) this ratio is lower (around 20 to 35%). This type of housing construction is commonly found in both rural and urban areas. This system of construction is not obviously the first choice for low-income families living in the villages but it's more widely spread in the cities where material and workmanship can be found cheaper. This construction type has been in practice for less than 50 years. Currently, this type of construction is being built. The question of how to estimate the rigidity of this type of connections has been the subject of many analytical and experimental research studies since the behavior of the structural system is a strong function of performance of the connections (References No.2). Buildings are constructed side-by-side forming a long block. They connect to each other without any seismic gap. Figure 1A: Typical Building Figure 1B: Typical Building Figure 2A: Key Load-Bearing Elements

3 Figure 2B: Vertical elevation of a typical show ing lateral bracing Figure 2C: Typical "Khorjini" connection 2. Architectural Aspects 2.1 Siting These buildings are typically found in flat, sloped and hilly terrain. They share common walls with adjacent buildings. 2.2 Building Configuration Buildings of this type are generally of rectangular shape, however there are also cases of irregularities in plan and height (Figure 7). In most of the cases openings are only in two parallel sides of the building plan as in the other two sides the building is standing side by side by the neighboring structure. X bracings are provided in the closed sides. 2.3 Functional Planning The main function of this building typology is mixed use (both commercial and residential use). There are many variations in building functions. Even hospitals, fire departments and government buildings may be found constructed earlier using this structural system. In a typical building of this type, there are no elevators and 1-2 fireprotected exit staircases. For most of the cases there is no emergency exit stairway. Units generally have only one main door which opens to the lobby or the main stairway. For taller buildings emergency exit and stairways are provided. 2.4 Modification to Building Adding stories on the top of the building, removing the partition walls.

4 Figure 3: Plan of a Typical Building 3. Structural Details 3.1 Structural System Material Type of Load-Bearing Structure # Subtypes Most appropriate type Masonry Stone Masonry Walls Adobe/ Earthen Walls Unreinforced masonry w alls Confined masonry Reinforced masonry Moment resisting frame 1 2 Rubble stone (field stone) in mud/lime mortar or w ithout mortar (usually w ith timber roof) Dressed stone masonry (in lime/cement mortar) 3 Mud w alls 4 Mud w alls w ith horizontal w ood elements 5 Adobe block w alls 6 Rammed earth/pise construction Brick masonry in mud/lime mortar Brick masonry in mud/lime mortar w ith vertical posts Brick masonry in lime/cement mortar Concrete block masonry in cement mortar Clay brick/tile masonry, w ith w ooden posts and beams Clay brick masonry, w ith concrete posts/tie columns and beams Concrete blocks, tie columns and beams Stone masonry in cement mortar Clay brick masonry in cement mortar Concrete block masonry in cement mortar 17 Flat slab structure Designed for gravity loads only, w ith URM infill w alls Designed for seismic effects, w ith URM infill w alls Designed for seismic effects, w ith structural infill w alls

5 21 Dual system Frame w ith shear w all Structural concrete Structural w all Steel Timber Other Precast concrete Moment-resisting frame Braced frame Structural w all Load-bearing timber frame Seismic protection systems Moment frame w ith in-situ shear w alls Moment frame w ith precast shear w alls 24 Moment frame 25 Prestressed moment frame w ith shear w alls 26 Large panel precast w alls Shear w all structure w ith w alls cast-in-situ Shear w all structure w ith precast w all panel structure 29 With brick masonry partitions 30 With cast in-situ concrete w alls 31 With lightw eight partitions Concentric connections in all panels Eccentric connections in a few panels 34 Bolted plate 35 Welded plate 36 Thatch Walls w ith bamboo/reed mesh and post (Wattle and Daub) Masonry w ith horizontal beams/planks at intermediate levels Post and beam frame (no special connections) Wood frame (w ith special connections) Stud-w all frame w ith plyw ood/gypsum board sheathing 42 Wooden panel w alls 43 Building protected w ith base-isolation systems 44 Building protected w ith seismic dampers Hybrid systems 45 other (described below ) As mentioned before, buildings of this type have X bracings in one direction (perpendicular to the street) and semirigid connections in the other direction. Please refer to Figure 5F. 3.2 Gravity Load-Resisting System The vertical load-resisting system is steel moment resisting frame. Consists of Steel frames (girders and columns with semi-rigid connections). 3.3 Lateral Load-Resisting System The lateral load-resisting system is steel moment resisting frame. 1- Light bracing, L or T sections, most of the times in one direction of the building only (perpendicular to street) where the building does not have any openings and hence connected to the adjacent building 2- On the other sides, lateral forces are resisted by means of semi-rigid connections "Khorjini" 3- Also un-reinforced brick infills between frame panels (without any gap) may contribute to the lateral force resistance but usually during seismic analysis and design process their effects are ignored and the R factor (inelastic reduction factor of seismic coefficient) is rather chosen based on the bare steel frame (as a common

6 mistake). According to the Iranian National Building Code, steel bracing should be provided in both directions of the building. 3.4 Building Dimensions The typical plan dimensions of these buildings are: lengths between 15 and 15 meters, and widths between 15 and 15 meters. The building has 2 to 5 storey(s). The typical span of the roofing/flooring system is 4 meters. Typical Plan Dimensions: It is on average. Variation of length is meters and width 9-15 meters. Typical Story Height: First floor usually has higher height, in the rage of about 4.0 m, for commercial use. Typical Span: Variation of span is 3-5 meters. The typical storey height in such buildings is 3 meters. The typical structural wall density is up to 5 %. 4%. 3.5 Floor and Roof System Material Description of floor/roof system Most appropriate floor Most appropriate roof Masonry Structural concrete Steel Timber Vaulted Composite system of concrete joists and masonry panels Solid slabs (cast-in-place) Waffle slabs (cast-in-place) Flat slabs (cast-in-place) Precast joist system Hollow core slab (precast) Solid slabs (precast) Beams and planks (precast) w ith concrete topping (cast-in-situ) Slabs (post-tensioned) Composite steel deck w ith concrete slab (cast-in-situ) Rammed earth w ith ballast and concrete or plaster finishing Wood planks or beams w ith ballast and concrete or plaster finishing Thatched roof supported on w ood purlins Wood shingle roof Wood planks or beams that support clay tiles Wood planks or beams supporting natural stones slates Wood planks or beams that support slate, metal, asbestos-cement or plastic corrugated sheets or tiles Wood plank, plyw ood or manufactured w ood panels on joists supported by beams or w alls Other Described below Masonry and steel jack arch structure. Masonry and steel jack arch structure Roofs/floors are very heavy and behave as flexible diaphragm unless special detailing is considered. The system consists of parallel roof steel beams at about one meter distance; beams support the shallow brick arches which are covered and leveled by gypsum finishing. 3.6 Foundation Type Description Most appropriate type Wall or column embedded in soil, w ithout footing Rubble stone, fieldstone

7 isolated footing Rubble stone, fieldstone strip footing Shallow foundation Reinforced-concrete isolated footing Deep foundation Reinforced-concrete strip footing Mat foundation No foundation Reinforced-concrete bearing piles Reinforced-concrete skin friction piles Steel bearing piles Steel skin friction piles Wood piles Cast-in-place concrete piers Caissons Other Described below Seismic problems related to the foundation system are rare. Single footings are connected to each other by strong ties. Figure 4: Critical Structural Detail - "Khorjini" connection 4. Socio-Economic Aspects 4.1 Number of H ousing Units and Inhabitants Each building typically has 2 housing unit(s). 2-6 units in each building. The number of inhabitants in a building during the day or business hours is The number of inhabitants during the evening and night is Roughly an Iranian family has 4~6 members. 4.2 Patterns of Occupancy Typically one family occupies one housing unit. 4.3 Economic Level of Inhabitants Income class Most appropriate type

8 a) very low -income class (very poor) b) low -income class (poor) c) middle-income class d) high-income class (rich) Economic Level: For Poor Class the Housing Unit Price is 10,000 and the Annual Income is 3,000. For Middle Class the Housing Unit Price is 60,000 and the Annual Income is 6,000. For Rich Class the Housing Unit Price is 250,000 and the Annual Income is 50,000. Ratio of housing unit price to annual income Most appropriate type 5:1 or w orse 4:1 3:1 1:1 or better What is a typical source of financing for buildings of this type? Ow ner financed Personal savings Informal netw ork: friends and relatives Small lending institutions / microfinance institutions Commercial banks/mortgages Employers Investment pools Government-ow ned housing Combination (explain below ) other (explain below ) Most appropriate type In each housing unit, there are 1 bathroom(s) without toilet(s), 1 toilet(s) only and 1 bathroom(s) including toilet(s). Bathrooms or latrines are rarely shared between units Ownership The type of ownership or occupancy is renting, outright ownership, ownership with debt (mortgage or other), individual ownership and long-term lease. Type of ownership or occupancy? Renting outright ow nership Ow nership w ith debt (mortgage or other) Individual ow nership Ow nership by a group or pool of persons Long-term lease other (explain below ) Most appropriate type

9 5. Seismic Vulnerability 5.1 Structural and Architectural Features Structural/ Architectural Feature Lateral load path Building Configuration Roof construction Floor construction Foundation performance Wall and frame structuresredundancy Statement The structure contains a complete load path for seismic force effects from any horizontal direction that serves to transfer inertial forces from the building to the foundation. Most appropriate type Yes No N/A The building is regular w ith regards to both the plan and the elevation. The roof diaphragm is considered to be rigid and it is expected that the roof structure w ill maintain its integrity, i.e. shape and form, during an earthquake of intensity expected in this area. The floor diaphragm(s) are considered to be rigid and it is expected that the floor structure(s) w ill maintain its integrity during an earthquake of intensity expected in this area. There is no evidence of excessive foundation movement (e.g. settlement) that w ould affect the integrity or performance of the structure in an earthquake. The number of lines of w alls or frames in each principal direction is greater than or equal to 2. Height-to-thickness ratio of the shear w alls at each floor level is: Wall proportions Foundation-w all connection Wall-roof connections Wall openings Less than 25 (concrete w alls); Less than 30 (reinforced masonry w alls); Less than 13 (unreinforced masonry w alls); Vertical load-bearing elements (columns, w alls) are attached to the foundations; concrete columns and w alls are dow eled into the foundation. Exterior w alls are anchored for out-of-plane seismic effects at each diaphragm level w ith metal anchors or straps The total w idth of door and w indow openings in a w all is: For brick masonry construction in cement mortar : less than ½ of the distance betw een the adjacent cross w alls; For adobe masonry, stone masonry and brick masonry in mud mortar: less than 1/3 of the distance betw een the adjacent cross w alls; Quality of building materials Quality of w orkmanship Maintenance For precast concrete w all structures: less than 3/4 of the length of a perimeter w all. Quality of building materials is considered to be adequate per the requirements of national codes and standards (an estimate). Quality of w orkmanship (based on visual inspection of few typical buildings) is considered to be good (per local construction standards). Buildings of this type are generally w ell maintained and there are no visible signs of deterioration of building elements (concrete, steel, timber)

10 Additional Comments 5.2 Seismic Features Structural Element Walls Frames (columns, beams) Roof and floors Connections Seismic Deficiency Cracking at the corners of un-reinforced masonry w alls. Out-ofplane collapse of unanchored w alls. Buckling/collapse of the first-storey columns due to soft story behavior. Buckling of the braces. Insufficient roof support, vulnerability height due to the w eak behavior of the heavy flexible roofs. Slippage betw een the girders and the columns. Insufficient sitting w idth for the girders on the columns angel connections. Earthquake Resilient Features Relatively enough in-plane stiffness, w hich contributes to the lateral resistance. Generally enough storey shear resistance. Shear failure is rare. N/A N/A Earthquake Damage Patterns Out of plane collapse, Classical X shear cracking. Buckling of the storey. Total/partial collapse. Excessive rotations, shear failure of the w elds, unsitting. Please refer to Figures. 5.3 Overall Seismic Vulnerability Rating The overall rating of the seismic vulnerability of the housing type is C: MEDIUM VULNERABILITY (i.e., moderate seismic performance), the lower bound (i.e., the worst possible) is B: MEDIUM-HIGH VULNERABILITY (i.e., poor seismic performance), and the upper bound (i.e., the best possible) is D: MEDIUM-LOW VULNERABILITY (i.e., good seismic performance). Vulnerability high medium-high medium medium-low low very low Vulnerability Class very poor poor moderate good very good excellent A B C D E F 5.4 H istory of Past Earthquakes Date Epicenter, region Magnitude Max. Intensity N, E, Rudbar-Manjil Bojnoord 6.1 N/A N/A N latitude and E longitude according to USGS, Ardekul 7.3 N/A 1997 Ardebil 5.5 N/A 1997 Ardebil magnitude: mb= Bojnoord magnitude: mb= Rudbar-Manjil magnitude: Mw=7.3 The same pattern of damage as mentioned in part 5. Please refer to the tectonic and seismicity maps of Iran, Figures: 6A, 6B, 6C and 6D.

11 Figure 5A: The 1990 Rudbar Manjil Earthquake, Partial Collapse of the Storey, Buckling of the Bracings, and permanent Sidesw ay (EERI Slide Collection) Figure 5B: Earthquake Damage Rudbar Manjil Earthquake (EERI Slide Collection) Figure 5C: Earthquake Damage, 1990 Rudbar Manjil Earthquake (EERI Slide Collection) Figure 5D: Earthquake Damage, 1990 Rudbar Manjil Earthquake (EERI Slide Collection) Figure 5E: Earthquake Damage, 1990 Rudbar Manjil Earthquake (EERI Slide Collection) Figure 5F: Earthquake Damage, 1990 Rudbar Manjil Earthquake (EERI Slide Collection) Figure 6A: Earthquake Map Figure 6B: Earthquake Map Figure 6C: Earthquake Map

12 Figure 6D: Earthquake Map Figure 6E: Earthquake Map Figure 7: A typical building 6. Construction 6.1 Building Materials Structural element Building material Characteristic strength Mix proportions/dimensions Walls Masonry (clay brick and cement/lime mortar) fc=200 kg/cm² 1:6, 55 X 110 X 220 mm N/A Foundation Reinforced Concrete f'c= 250 kg/cm² 1:2:4 N/A Frames (beams & columns) Roof and floor(s) Steel fy= 2400kg/cm² N/A N/A Steel Beams and Masonry Infill, (Brick and Gypsum) N/A N/A N/A Comments 6.2 Builder Sometimes, but these days it is typically designed and built by the developers. 6.3 Construction Process, Problems and Phasing In most of the cases, owner or a contractor on behalf is in charge of the construction. The construction process has 3 main parts, excavation and foundation construction, steel frames erection, masonry works and the installation of electrical and mechanical systems. Simple machinery is used throughout the construction like a small crane. The construction of this type of housing takes place incrementally over time. Typically, the building is originally not designed for its final constructed size. NA. 6.4 Design and Construction Expertise Usually the whole process of construction is being done by a team of workers (not always certified workers). A

13 registered engineer checks the final design. In spite of many lessons learnt in the previous earthquakes proving poor performance of this structural system, many engineers still design the buildings using this system. Lack of quality control by the engineers during design and construction is obvious. 6.5 Building Codes and Standards This construction type is addressed by the codes/standards of the country. "Iranian Code of Practice For Seismic Resistance Design of Buildings, 2nd Edition 1999, Iranian National Building Code"; special detailing required to improved the seismic performance are addressed in the appendix. The year the first code/standard addressing this type of construction issued was N.A. The most recent code/standard addressing this construction type issued was Title of the code or standard: "Iranian Code of Practice For Seismic Resistance Design of Buildings, 2nd Edition 1999, Iranian National Building Code"; special detailing required to improved the seismic performance are addressed in the appendix. Year the first code/standard addressing this type of construction issued: 1999 National building code, material codes and seismic codes/standards: N.A. The new edition of the "Iranian Code of Practice for Seismic Resistant Design of Buildings-Standard No. 2800", which is a very well prepared code, was subjected to the Iranian government approval in December However there are not much strong interest among building officials towards the enforcement of the code and quality control of the constructed infrastructures in many parts of the country is low. "In general the building departments of municipalities have the responsibility to check and approve the design process, however the design engineer holds the responsibility for the projects. When the construction is completed then the municipal authorities check the finished project to issue the occupancy permit." (Ref: Building Permits and Development Control Rules This type of construction is an engineered, and not authorized as per development control rules. N.A. Building permits are required to build this housing type. 6.7 Building Maintenance Typically, the building of this housing type is maintained by Owner(s). N.A. 6.8 Construction Economics 2,000, Rials/m² (US$ /m²) (Note: Exchange rate of US$ 1.00 = 8,000 Rials is used). Foundation: 20 Days - 1 Technical Staff - 5 Workers Steel Structure Erections and Masonry Work: 3 Months - 2 Technical Staff - 10 Workers Final Finishing: 4 Months - 2 Technical Staff - 6 Workers. 7. Insurance Earthquake insurance for this construction type is typically available. For seismically strengthened existing buildings or new buildings incorporating seismically resilient features, an insurance premium discount or more complete coverage is unavailable. 8. Strengthening

14 8.1 Description of Seismic Streng thening Provisions Strengthening of Existing Construction : Seismic Deficiency Description of Seismic Strengthening provisions used Out of plane w all collapse/ creaking Addition of concentric bracing to the spans Partial/ total collapse of the stories, soft storey Adding concentric bracings Roof collapse Connection unsitting/slippage Horizontal bracings w elded on the roof/floor beams Strengthening the connection, connection confinement using steel plates No practical example is unfortunately available to the author at this time however there are plenty research projects going on or already completed on this issues. Please refer to reference no. 5: Seismic Strengthening Adopted Has seismic strengthening described in the above table been performed in design and construction practice, and if so, to what extent? Yes, depending on the importance of the project different retrofitting strategies could be implemented. Was the work done as a mitigation effort on an undamaged building, or as repair following an earthquake? Mitigation on an existing undamaged building. 8.3 Construction and Performance of Seismic Strengthening Who performed the construction seismic retrofit measures: a contractor, or owner/user? Was an architect or engineer involved? Retrofit designed by an engineer, constructed by a contractor under supervision of the engineer. What was the performance of retrofitted buildings of this type in subsequent earthquakes? Relatively good when the code considerations are taken into account. Reference(s) 1. Iranian Code of Practice for Seismic Resistant Design of Buildings-Standard No The Seismic Design Handbook Naeim,F. Second Edition, ICBO, SEA and Kluw er Publishers sharif.ac.ir/~civilinfo/thesis/structural99.htm

15 8. seismo.ethz.ch/gshap/iran/report.html 9. geohaz.org/radius/tehran/ seismo.univ.trieste.it/cdrom/reports/qr230.htm Author(s) 1. Arzhang Alimoradi, John A. Martin & Assoc.,, USA Reviewer(s) 1. Farzad Naeim Vice President, John A. Martin & Associates Los Angeles CA 90015, USA FAX: (213) Save page as